Put a pint of demi-glace (No. 9) into a stewpan, place it over the fire,
keeping it stirred until it has reduced one third; have four
middling-sized preserved French truffles cut into slices, which throw
into the sauce, add a little sugar, and take it from the fire, not
allowing it to boil after the truffles are in; it is then ready to serve
where directed: by this simple method you retain the full flavour of the
truffles, and keep them tender. Sauce aux truffles may also be made
white by using white sauce (No. 7), instead of demi-glace, and finishing
with half a gill of cream, but it requires to be rather thicker than the
brown. When brown, neither this sauce nor the following must be too
thick.